Deadline.com said Moore was a surprise guest who teased her ex-partner about his age, baldness, music, movie career and relationship skills in front of a crowd that included Willis' current wife, model Emma Heming.
"I look at our marriage like The Sixth Sense," TMZ quoted Moore as saying. "You were dead the whole time."
Moore was married to Willis 1987 through 2000. Willis and Heming tied the knot in 2009. They have two daughters -- Mabel, 6 and Evelyn, 4.
Also on hand to mercilessly mock the action movie star at the roast were his former castmates Joseph Gordon-Levitt, Edward Norton and Cybill Shepherd, as well as comedian Jeff Ross, basketball icon and television personality Dennis Rodman, and media mogul Martha Stewart.
The Comedy Central special is to air on July 29.